Firefox and passwords-help

My pc running Firefox saves all passwords and logins names if asked . great but I want to delete one. Not change it or anything, just delete it. How? I think I can delete the lot but I only want to do one.

Reason? Banned from a forum for giving the owners, a magazine, a few home truths. Now whenever I want to visit the forum as a guest, to check on something, I can't as my pc automatically tries to log me in and thus I am recognised and blocked.
anyway, how can I remove login details. I have done in on IE ok.

Tools> options> security> saved passwords> highlight the chosen password and delete.

I think

Tools->Options->Security->Saved Passwords

Ta but that's not it. The site/forum/password isn't on that list. I have removed it from that already. any other ideas?

check for cookies from their site too

no cookies except this site as I can't login without it.

Download another browser…

Sort of sorted. I have to ban all cookies then it will open. I then have to allow this site for it to work. Ta people.